1. Field of the Invention
The present invention relates to an automatic transmission system for vehicles, in which the gear-shift mode is determined in accordance with the position selected by a selector lever.
2. Description of the Prior Art
Conventional automatic transmission systems for vehicles in which the gear-shift mode is determined in response to a signal indicating the position of the selector lever are widely used. In such type of automatic transmission system the selector lever is coupled with a position detector comprising, for example, variable resistors, switches or the like, and an electric signal produced by the position detector indicating the position of the selector lever is applied to a control unit of the automatic transmission system, whereby the gear-shift mode of the system is determined in accordance with the set position of the selector lever. Accordingly, it becomes impossible to control the change of the gear-shift mode if a malfunction or trouble arises in the elements forming the position detector or the wiring system thereof.
The overcome this disadvantage, Japanese Patent Application Public Disclosure No. 157441/86 discloses an arrangement, for example, in which a position detector is provided with a plurality of position switches including two reverse position switches for indicating the reverse mode when the two reverse position switches are simultaneously turned on and the transmission can be shifted to the neutral or one of the forward positions in the case of a malfunction of either or both of the position switches, namely at any time other than when the two reverse position switches are simultaneously turned on.
However, with the proposed arrangement, in the case where a malfunction arises in the position detector just after the selector lever is positioned at the neutral (N) position, the neutral (N) position is determined as the position just before the occurrence of the malfunction, so that the neutral position is selected in priority to the other positions even if the drive (D) position for automatic gear-shifting operation is selected by the driver. This will make it impossible to drive off the vehicle.